Update PULL_REQUEST_TEMPLATE.md (#41812)
Summary:
**Summary**
This commit updates the repository's pull request template to remind contributors to tag the issue that their pull request addresses.
**Fixes**
This commit fixes https://github.com/pytorch/pytorch/issues/35319.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/41812
Reviewed By: gmagogsfm
Differential Revision: D22667902
Pulled By: SplitInfinity
fbshipit-source-id: cda5ff7cbbbfeb89c589fd0dfd378bf73a59d77b
